Hydrogen (H2) is a colorless, odorless, tasteless,
flammable and nontoxic gas at atmospheric temperatures and pressures. It
is the most abundant element in the universe, but is almost absent from
the atmosphere as individual molecules in the upper atmosphere can gain
high velocities during collisions with heavier molecules, and become
ejected from the atmosphere. It is still quite abundant on Earth, but as
part of compounds such as water.

Hydrogen burns in air with a pale blue, almost invisible flame. Hydrogen
is the lightest of all gases, approximately one-fifteenth as heavy as
air. Hydrogen ignites easily and forms, together with oxygen or air,
an explosive gas (oxy-hydrogen).

Hydrogen has the
highest combustion energy release per unit of weight of any commonly occurring
material. This property makes it the fuel of choice for upper stages
of multi-stage rockets.

Hydrogen has the lowest boiling point of any element except helium.
When cooled to its boiling point, -252.76o C
(-422.93o F) hydrogen becomes a transparent, odorless liquid that is only
one-fourteenth as heavy as water. Liquid hydrogen is not corrosive or particularly reactive. When converted from liquid to gas, hydrogen expands approximately 840 times.
Its low boiling point and low density result in liquid hydrogen spills
dispersing rapidly.

The most common large-scale process for manufacturing hydrogen is steam reforming of hydrocarbons, in particular,
natural gas (mostly methane). Other methods used for hydrogen production methods include
generation by partial oxidation of coal or hydrocarbons,
electrolysis of water, recovery of byproduct hydrogen from electrolytic
cells used to produce chlorine and other products, and dissociation of
ammonia. Hydrogen is recovered
for internal use and sale from various refinery and chemical
streams, typically purge gas, tail gas, fuel gas
or other contaminated or low-valued streams. Purification methods include pressure swing adsorption (PSA), cryogenic
separation and membrane gas separation.

Many hydrogen gas users purchase it as a liquid, which can be
vaporized as needed, instead of producing it on their own site. Liquefaction of gaseous hydrogen is a multi-stage process using several
refrigerants and compression/ expansion loops to produce extreme cold. As
part of the process, the hydrogen passes through "ortho/ para" conversion
catalyst beds that convert most of the "ortho" hydrogen to the "para"
form. These two types of diatomic hydrogen have different energy states.
In "ortho" hydrogen, which is the most common form at room
temperature, making up approximately 75% of the mixture, the
nuclei have
parallel proton spins. In "para" hydrogen the
nuclei have anti-parallel proton spins. "Ortho" hydrogen is
less stable than "para" at liquid hydrogen temperatures. The
equilibrium mix is almost all para-hydrogen which means that over time,
any liquefiied ortho hydrogen will change to the "para" form.
This spontaneous change releases energy, and results in vaporizing a
portion of the liquid in storage. To minimize this, a catalytic
conversion step is used to maximize the percentage of para hydrogen sent
to storge. A commonly used catalyst is hydrous ferric oxide.

Some industrial processes with relatively small hydrogen requirements may
choose to produce some or all of their needs using compact generators.
In the past, ammonia dissociation was a common technology choice.
More recently,
improvements in small packaged electrolytic and hydrocarbon reforming
systems have made these routes to small volume hydrogen production
increasingly attractive. In some cases these packaged systems may be the sole
source of hydrogen at a site, or they may be used to supplement and/or
back-up other supply sources.

Highly packaged, compact hydrocarbon reformer units have made it possible
to utilize on-site hydrocarbon
reforming at much lower production rates than were concidered
commercially feasible only a few years ago. Similarly, increasingly energy
efficient electrolytic hydrogen production units, which use water and
electric power to
produce high purity hydrogen at common in-plant distribution pressures,
are being applied at amenable hydrogen user sites.

Much
has been said about hydrogen being the "fuel of the
future" due to its abundance and its non-polluting combustion products.
Less has been said about the fact that other forms of energy must be
consumed
to produce the hydrogen which will be used as fuel. Most hydrogen is
derived from compounds such as water or methane, and energy is required to
break the hydrogen free from these compounds, then separate, purify,
compress and/ or liquefy the hydrogen for storage and transportation to
usage points. Widespread production, distribution and use of hydrogen will
require many innovations and investments to be made in efficient and
environmentally-acceptable production systems, transportation systems,
storage systems and usage devices.

Currently, there is a great deal of interest in hydrogen fuel cell technology development
and investigations into unconventional or specialized hydrogen storage
systems. New technologies and
equipment developed to support these applications will
undoubtedly find uses in industry as well.

Hydrogen is mixed with inert gases to obtain a reducing atmosphere, which
is required for many applications in the metallurgical industry, such as
heat treating steel and welding. It is often
used in annealing stainless steel alloys, magnetic steel alloys, sintering
and copper brazing.

Hydrogen can be produced by dissociation of ammonia at
about 1800˚F with the aid of a catalyst - which
results in a mix of 75% hydrogen and 25% mononuclear nitrogen (N rather
than N2). The mix is used as a protective atmosphere for applications such
as brazing or bright annealing.

Chemicals, Pharmaceuticals and Petroleum:

Hydrogen is used in large quantities as a raw material in the chemical synthesis of ammonia,
methanol, hydrogen peroxide, polymers, and solvents.

In refineries, it is
used to remove the sulfur that contained in crude oil. Hydrogen is
catalytically combined with various intermediate processing streams and is used,
in conjunction with catalytic cracking operations, to convert heavy and unsaturated
compounds to lighter and more stable compounds.

The pharmaceutical
industry uses hydrogen to manufacture vitamins and other pharmaceutical
products.

Large quantities of hydrogen are used to purify gases (e.g. argon)
that contain trace amounts of oxygen, using catalytic combination of the
oxygen and hydrogen followed by removal of the resulting
water.

Glass
and Ceramics:

In float glass manufacturing, hydrogen is required to prevent oxidation of
the large tin bath.

Food
and Beverages:

It is used to hydrogenate unsaturated fatty acids in animal and
vegetable oils, producing solid fats for margarine and other food
products.

Electronics:

Hydrogen is used as a carrier gas for such active trace elements as arsine and phospine, in the manufacture of semi-conducting layers in integrated circuits.

Miscellaneous:

Generators in large power plants are often cooled with hydrogen, since the gas processes high thermal conductivity and offers low friction resistance.

Liquid hydrogen is used as a rocket fuel.

The nuclear fuel industry uses hydrogen as a protective atmosphere in the
fabrication of fuel rods.